A bar of Green and Black's chocolate. Few people were aware its parent company is Kraft. Photograph: Graeme Robertson

Most consumers are ignorant of the multinational parent companies behind so-called ethical brands such as Rachel's Organic, Seeds of Change and Green & Black's, according to a survey due to be published this week by the consumer organisation Which?.

Three-quarters of the people questioned also believe companies should be clear about ownership on the brand's packaging, but the survey, to published on Thursday, reveals that corporate parents often keep quiet about their ethical offspring.

Of the 2,110 Which? members surveyed, between 74% (for Green & Black's) and 96% (for Copella) were unaware of the big names behind 10 popular ethical brands. And, once they found out, of those whose opinion changed, more had a negative reaction than a positive one. "Consumers are being misled," said one respondent while another commented: "I feel conned."

Two-thirds of of those surveyed rated environmental and ethical issues as important when deciding which brands to buy, but they viewed ethical brands and their parent companies quite differently. For example, 71% associate Seeds of Change with environmental responsibility, compared with only 15% for its parent company, the confectionery giant Mars. Some Which? members said they were concerned that large companies might be more concerned with profits than ethics.

Prof Craig Smith, the chair of ethics and social responsibility at the international Insead Business School, said there was a danger that parent companies might try to change the ethical company and "dilute" its values. But he added: "Parent companies can give ethical brands the resources they need to expand their business and promote ethical products and environmental issues to a wider audience."

Among the companies scrutinised by Which? is Green & Black's, founded in 1991. It produces premium chocolate using organic ingredients that are "ethically sourced". It was bought by Cadbury in 2005, which was then acquired by Kraft in 2010. Which? members view the two companies quite differently. For example, only 11% feel Kraft to be socially responsible compared with 44% for Green & Black's. And only 21% view Kraft as trustworthy, compared with 53% for Green & Black's.

Mark Palmer, the global brand director at Green & Black's, said: "There haven't been any changes to the specifications or recipes of our chocolate. Neither have there been any changes to [our] philosophy and values."